Providing more ammunition for amino acid PET imaging

A novel amino acid agent could zero in on cancerous tumors and provide a much longer half-life than the status quo, according to a study published in the April issue of the Journal of Nuclear Medicine.

The diversification of imaging agents is an important endeavor for the field of molecular medicine, as the limitations of FDG and the sensitivity and specificity of PET become increasingly clear. Researchers are looking to a range of new agents that work in very different ways to improve the mapping and staging of disease. Amino acid imaging is just one of these emerging techniques.

Bromine-76 radiolabeled agents could be an ideal solution because they have a 16.2-hour half-life. They are therefore highly competitive compared to commercially available agents such as those radiolabeled with carbon-11 and fluorine-18 isotopes, which decay in minutes.

Hirofumi Hanaoka, PhD, from the department of bioimaging information analysis at Gunma University Graduate School of Medicine in Maebashi, Japan, and colleagues have prepared two new Br-76 labeled agents to test the waters.

“C-11 and F-18 labeled tracers are not good for delivery due to their short half-lives,” explained Hanaoka in an interview with Health Imaging. “In many cases, amino acid tracers are better than FDG. We think widely usable amino acid [agents] will provide significant benefit to tumor diagnoses for many cancer patients.”

The researchers developed these two agents, 2-76Br-bromo-a-methyl-L-phenylalanine (2-76Br-BAMP) and 4-76Br-bromo-α-methyl-L-phenylalanine (4-76Br-BAMP), due to their encouraging chemical stability and tumor specificity. They compared their usefulness for the preclinical mapping of LS180 colon adenocarcinoma.

Results showed that 2-76Br-BAMP was the superior imaging agent and it could have significant potential for clinical use.

“In the biodistribution studies, 2-77Br-BAMP showed more rapid blood clearance and lower renal accumulation compared to 4-77Br-BAMP,” wrote Hanaoka and colleagues. “More than 90 percent of the injected radioactivity was excreted in the urine by [6 hours] after the injection of 2-77Br-BAMP.”

Still, physicians face a few challenges before 2-77Br-BAMP could be dispersed for widespread use.

“The availability of Br-76 is limited; it will be difficult to bring Br-76-labeled tracers to market, but due to the relatively long half-life of Br-76, it may be possible for private industry and/or large facilities to produce Br-76 labeled tracers for delivery to medical centers,” wrote Hanaoka and colleagues.

While the agent is currently not approved for general use, Hanaoka is making plans to begin clinical studies within the next three years to get a better sense of the agent’s value for oncologic imaging.